Quartz, glass and other silica-based materials are often processed in the form of rods and tubes by heating the material in a furnace and then drawing or extruding the material through a die or orifice. Because of its high temperature strength and creep resistance, tungsten has been used to form the furnace structure and components that contact silica-based materials during processing, including drawing dies and extrusion nozzles. However, tungsten tends to react with silica, generating undesirable tungsten-based inclusions and defects in the processed material, as well as leading to degradation of the tungsten-based component. Defects in materials generated by reactions with tungsten are highly undesirable for many quartz applications, particularly in the semiconductor and lamp industries. The reactivity of tungsten with silica also reduces the service life of the tungsten components.
In response, the prior art has used rhenium to protect tungsten nozzles on the basis that rhenium is less reactive with silica than tungsten. An existing method has been to form a rhenium tube by producing a blank of 90% theoretical density using a powder metallurgy (PM) process. The blank is then rolled to form a tube that can be inserted into an appropriately sized bore formed in a PM tungsten nozzle that was pre-sintered to near 100% density. After installation, the rhenium tube is diffusion bonded to the tungsten nozzle.
While being less reactive to silica-containing materials, rhenium tubes produced and installed in the manner described above are prone to cracking during use of the tungsten nozzles at high service temperatures. Accordingly, it would be desirable if improved components were available for use in the processing of silica-based products.